can thermal cameras see through walls
Thermal imagers cannot clearly see through ordinary walls. Their "see-through" capabilities have clear physical limitations, directly related to their operating principle and the physical properties of the wall.
To understand this, we first need to understand the basic working principle of a thermal imager: it does not rely on visible light, but instead receives infrared light (thermal radiation) emitted by objects to form images, ultimately converting objects of different temperatures into thermal images visible to the naked eye (the higher the temperature, the redder and whiter the image; the lower the temperature, the bluer and darker the image).
Ordinary walls (such as brick, concrete, and wood) block thermal imagers' "observation" in two key ways:
They have very low infrared penetration.
Wall materials (such as brick, concrete, and drywall) are highly infrared-blocking. When infrared light (especially the "mid-wave infrared" and "long-wave infrared" that thermal imagers primarily detect) hits the wall, it is mostly absorbed or reflected, leaving only a tiny amount penetrating. This amount of penetration is far insufficient to carry temperature details of objects on the other side of the wall, making it impossible to form a clear image. For example, walls themselves generate their own thermal radiation signatures due to ambient temperature (e.g., low temperatures outside, heated indoors). Consequently, a thermal imager can only see the "temperature distribution on the wall's surface" (e.g., cracks in the wall may be slightly cooler and appear darker), but cannot see people or furniture within the wall.
Interference from the wall's own thermal radiation
Even if a tiny amount of infrared light penetrates the wall, the wall itself will continue to emit thermal radiation, which is far more intense than the tiny amount of infrared light that penetrates, completely masking the thermal information of objects within the wall and rendering the thermal imager unable to discern.
Special Case: What "obstacles" can be "penetrated" by thermal imagers?
Thermal imagers are not completely incapable of "penetrating" objects, but they can only see through materials with minimal infrared resistance and are extremely thin. Furthermore, the "penetrating" effect is merely a blurry temperature profile, not a clear image:
Extremely thin plastic film, single-layer glass (glass blocks long-wave infrared radiation to some extent, but thin glass allows some medium-wave infrared radiation to pass through, blurring the view of hot objects behind the glass, such as observing a heater through a window);
Thin fabric (such as a single layer of cotton, which can blur the temperature distribution of a person beneath the fabric, but not reveal details).
These situations are fundamentally different from "penetrating walls"—the thickness and material density of a wall determine its fundamental infrared resistance.
Summary
The core function of a thermal imager is to detect thermal radiation from an object's surface, not to see through solid obstacles. For ordinary residential and building walls, it cannot see clearly what is inside, but can only reflect the temperature characteristics of the wall itself.
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